Apparatus and method for manufacturing copper clad laminate with improved peel strength

ABSTRACT

The present invention relates to an apparatus and method for manufacturing a copper clad laminate, which can achieve a substantial improvement in the peel strength between a thermoplastic liquid crystal polymer and a copper foil. The apparatus comprises: a coating means for thinly coating the surface of a copper foil with a thermoplastic liquid crystal polymer solution; a solvent removal means for drying the coated liquid crystal polymer solution to remove the solvent of the coated solution; and a thermal pressing means for laminating and thermally pressing a thermoplastic liquid crystal polymer film onto the copper foil using heating rolls so as to make a copper clad laminate.

INCORPORATION BY REFERENCE

The present application claims priority under 35 U.S.C. §119 to KoreanPatent Application No. 10-2004-0106433 filed on Dec. 15, 2004. Thecontent of the application is incorporated herein by reference in itsentirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an apparatus and method formanufacturing a copper clad laminate, and more particularly to anapparatus and method for manufacturing a copper clad laminate, which cansubstantially improve the peel strength between a thermoplastic liquidcrystal polymer and a copper foil.

2. Description of the Prior Art

In general, printed circuit boards refer to products obtained by formingcircuits on a copper clad laminate composed of a copper foil laminatedon a material, such as paper phenol resin or glass epoxy resin, usingtechniques such as patterning and etching.

With the development of electronic technology, recent printed circuitboards become lighter in weight and smaller in size in order to mountparts at high integration density, and are of increasing importance asthe basic factor for increasing integration density.

With this recent importance of printed circuit boards, copper cladlaminates are also manufactured and used in various manners.Particularly with a surprising increase in the integration density ofsemiconductor integrated circuits and the development of surfacemounting technology for directly mounting small chip parts, reductionsin the weight and size of electronic products, such as mobilecommunication devices, are rapidly made. For this reason, the use offlexible printed circuit boards, which are mounted in spaces withinelectronic products much more easily than are existing rigid printedcircuit boards (rigid PCBs), is increasing. Also, to achieve thehigh-density integration (HDI) of circuit patterns, the use of amulti-layer flexible PCB or a rigid-flexible multi-layer PCB is nowrapidly increasing.

Meanwhile, as the material of these flexible and rigid-flexible printedcircuit boards, polyimide is generally used. However, the polyimide usedhas a problem in dimensional stability due to high water absorptionrate, and a shortcoming in that it shows reductions in dielectricconstant (Dk) and dissipation factor (Df) in a high-frequency range (GHzrange). For these reasons, a thermoplastic liquid crystal polymer (LCP)is spotlighted as a substitute material for the polyimide.

The thermoplastic liquid crystal polymer has high dimensional stabilityresulting from low water absorption rate (<0.1%), a thermal expansioncoefficient similar to copper foil (16-18 ppm/° C.), and a lowdielectric constant (Dk) and dissipation factor (Df) in a high-frequencyrange (GHz range). In view of these advantages, the thermoplastic liquidcrystal polymer is expected not only to substitute for polyimide in theflexible and flexible-rigid printed circuit boards, but also to beapplied as insulation material in HDI for mobile phones, semiconductors(e.g., BGA, CSP, etc.), network substrates, and the like.

Currently, leading global chemical companies, includingTicona-Polyplastics, Sumitomo and Dupont, produce and sell thermoplasticliquid crystal polymer resins. Also, companies, including Kuraray,Nippon Steel Chemical Co., Rogers, and Goretex, manufacture insulationfilms and flexible clad laminates (FCCL) for application to boardmaterials by using the thermoplastic liquid crystal polymer resin.

Prior methods for manufacturing the flexible copper clad laminates canbe broadly divided into the following two categories: (1) amanufacturing method comprising forming a roughness on the surface of acopper foil (12 or 18 μm) and thermally pressing a thermoplastic liquidcrystal polymer film onto the copper foil by means of two heating rolls;and (2) a manufacturing method with the use of the press method used inthe manufacturing of copper clad laminates, such as FR4 laminates.

The first method of manufacturing copper clad laminates by forming aroughness on the surface of a copper foil and thermally pressing athermoplastic liquid crystal polymer film onto the copper foil is shownin FIG. 1. As shown in FIG. 1, in order to form circuit patterns on oneor both sides of thermoplastic liquid crystal polymer film 110 which istransferred between reels 124 a and 124 b by drive rolls 126 a and 126b, copper foil 112 passes through upper and lower press rolls 120 and122 and, at the same time, is laminated onto the thermoplastic liquidcrystal polymer film 110, thus manufacturing flexible copper cladlaminate (FCCL) 100.

The second method of manufacturing copper clad laminates using the pressmethod used in the manufacturing of FR4 copper clad laminates is shownin FIG. 2A. As shown in FIG. 2A, the manufacturing method comprises thesteps of: preparing first and second solid metal press plates eachhaving a flat surface; preparing first and second flat heating plates;preparing first and second copper foils; and sandwiching a thermoplasticliquid crystal polymer film between the first and second copper foilsand thermally pressing the first and second copper foils onto thethermoplastic liquid crystal polymer film in a vacuum by the first andsecond metal press plates, thus forming a flexible copper clad laminate.

In the press method, among the prior methods, there is an advantage inthat the copper clad laminate can be easily manufactured because thecopper foils and the thermoplastic liquid crystal polymer film arepressed at the same time in a manner similar to the prior method ofmanufacturing copper clad laminates, such as FR4 laminates. However, thepress method has shortcomings in that it is difficult to obtain productshaving uniform dimensional stability due to a difference in properties(e.g., thermal deformation with temperature) between the thermoplasticliquid crystal polymer and FR4, and that it has lower productivity thanthe method of manufacturing copper clad laminates by thermal pressingwith the heating rolls.

Particularly for flexible or rigid-flexible PCBs, conversion to aroll-to-roll process is expected, and thus, there is a need for a methodcapable of manufacturing flexible clad laminates in a roll form.

In addition, the method with the use of heating rolls comprises forminga roughness on the surface of the copper foil in order to increase thepeel strength between the copper foil and the thermoplastic liquidcrystal polymer film, followed by thermal pressing. Also, in view of theproblem of low dimensional stability which can occur in the pressmethod, a preheating step is conducted before the thermal pressing inorder to solve the problem of rapid thermal expansion caused by thethermal pressing at high temperature.

Kuraray Co., Ltd., Japan, has a number of pending patent applicationsrelating to copper clad laminates manufactured with the thermoplasticliquid crystal polymer film and the copper foil (Japanese PatentLaid-Open Publication Nos. 2000-263577, 2000-343610, 2001-079946,2001-079947, and 2003′-103700).

However, in the copper clad laminates manufactured by the press methodand the thermal pressing method with the use of heating rolls, the peelstrength between the copper foil and the thermoplastic liquid crystalpolymer film is shown to be much lower than 0.8 kN/m which is theminimum level applicable to PCB materials. Accordingly, a need toimprove this peel strength now exists.

SUMMARY OF THE INVENTION

Accordingly, the present invention has been made to solve the aboveproblems occurring in the prior art, and an object of the presentinvention is to provide an apparatus and method for manufacturing acopper clad laminate, which can substantially improve the peel strengthbetween a thermoplastic liquid crystal polymer and a copper foil so thatthe copper clad laminate is applicable to PCB materials.

To achieve the above object, in one embodiment, the present inventionprovides an apparatus for manufacturing a copper clad laminate,comprising: a coating means for thinly coating the surface of a copperfoil with a thermoplastic liquid crystal polymer solution; a solventremoval means for drying the coated liquid crystal polymer solution toremove the solvent of the coated polymer solution; and a thermalpressing means for laminating and thermally pressing a thermoplasticliquid crystal polymer film onto the copper foil by heating rolls so asto make a copper clad laminate.

In another embodiment, the present invention provides a method formanufacturing a copper clad laminate, comprising the steps of: coatingthe surface of a copper foil having a roughness formed thereon with athermoplastic liquid crystal polymer solution to small thickness; dryingthe coated liquid crystal polymer solution to remove the solvent of thepolymer solution; and laminating and thermally pressing a thermoplasticliquid crystal polymer film onto the copper foil by heating rolls so asto make a copper clad laminate.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will be more clearly understood from the following detaileddescription taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 illustrates a method for manufacturing copper clad laminatesusing rolls according to the prior art;

FIGS. 2A to 2B illustrate a method for manufacturing copper cladlaminates using presses according to the prior art;

FIG. 3 shows the construction of an apparatus for manufacturing a copperclad laminate having improved peel strength, according to one embodimentof the present invention; and

FIG. 4 is a flow chart showing a method for manufacturing a copper cladlaminate having improved peel strength, according to one embodiment ofthe present invention.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, an embodiment of the present invention will be described indetail with reference to FIGS. 3 and 4.

FIG. 3 shows the construction of an apparatus for manufacturing a copperclad laminate according to one embodiment of the present invention. Asshown in FIG. 3, the manufacturing apparatus comprises: a copper foilfeed roll 301; a thermoplastic liquid crystal polymer film feed roll302; a copper clad laminate storage roll 303; a heating section 324 forheating copper foil 313 coated with a thermoplastic liquid crystalpolymer; copper foil transfer rolls 326 a and 326 b for allowing thecopper foil 310 fed from the copper foil feed roll 301 to pass through acoating section 328; heating rolls 320 and 322 for laminating athermoplastic liquid crystal polymer film onto the thermoplastic liquidcrystal polymer-coated copper foil passed through the heating section324 and pressing and heating the laminate; and a copper clad laminatetransfer roll 326 c for transferring the copper clad laminate 314discharged from the heating rolls 320 and 322 to the copper cladlaminate storage roll 303.

As the copper foil is fed from the copper foil feed roll 301, the copperfoil transfer rolls 326 a and 326 b cause the copper foil 310 to passthrough the coating section 328. At this time, the copper foil 310 fedfrom the copper foil feed roll 301 has a roughness formed on the surfacethereof, and due to the roughness, the thermoplastic liquid crystalpolymer solution to be applied later will adhere well to the surface ofthe copper foil.

Then, in the coating section 328, the copper foil 310 is thinly coatedwith the thermoplastic liquid crystal polymer solution. Thanks to thecoated polymer solution, the peel strength of a manufactured copper cladlaminate can be highly improved compared to the prior art.

The thermoplastic liquid crystal polymer solution may contain filler inan amount of 0-30% by volume, in which the filler serves to reduce thethermal expansion coefficient and curling events.

Examples of the filler, which can be used in the present embodiment,include inorganic materials, such as silica, alumina, titania, andcalcium carbonate, and organic materials, such as carbon and graphite.Coating the liquid crystal polymer solution on the copper foil havingthe roughness formed on the surface thereof may be performed using aroller coating, dip coating, spray coating, spinner coating, curtaincoating, slot coating or screen printing processes.

After coating the copper foil with the thermoplastic liquid crystalpolymer solution, the solvent of the polymer solution is removed bypre-drying at 50-100° C. for 30 minutes to 2 hours in the heatingsection 324, and then, completely drying at 250-300° C. for 1-4 hours.

Then, by the pressing rolls 320 and 322, the thermoplastic liquidcrystal polymer film 312 fed from the thermoplastic liquid crystalpolymer film feed roll 302 is laminated onto the thermoplastic liquidcrystal solution-coated dried copper foil 313 passed through the coatingsection, and then, the laminate undergoes thermal pressing (i.e.,heating and pressing), thus making the copper clad laminate 314.

In the process where the thermoplastic liquid crystal polymer film 312is thermally pressed onto the copper foil 313 by the heating rolls 320and 322, the thermal pressing is carried out at a higher temperaturethan the thermal deformation temperature of the liquid crystal polymerfilm. The reason why the thermal pressing process following the coatingprocess is carried out as described above is that the copper cladlaminate manufactured only by coating without thermal pressing will havethe following problems: the problems of the surface flatness andthickness uniformity of a copper clad laminate; and the problem ofcurling caused by the shrinkage of the thermoplastic liquid crystalpolymer during the drying process for removing the solvent.

Because the thermoplastic liquid crystal polymer solution applied in thecoating section and the thermoplastic liquid polymer film thermallypressed by the heating rolls 320 and 322 are made of the same material,sufficient adhesion therebetween can be achieved by thermal pressing ata temperature higher than their thermal deformation temperature, a speedof 1-5 m/min, and a pressure of 1-10 MPa.

FIG. 4 is a flow chart showing a method for manufacturing a copper cladlaminate having improved peel strength, according to one embodiment ofthe present invention.

As shown in FIG. 4, as a copper foil with a thickness of, for example,12 μM, is fed from the copper foil feed roll, the copper foil transferrolls cause the copper foil to pass through the coating section. In thecoating section, the copper foil is thinly coated with a thermoplasticcrystal polymer solution (step S110).

The thermoplastic liquid crystal polymer solution may contain filler inan amount of 0-30% by volume, in which the filler can serve to reducethe coefficient of thermal expansion.

Then, in the heating section, the solvent of the coated thermoplasticliquid crystal polymer solution is removed by, for example, pre-dryingat 80° C. for 1 hour and then completely drying at 250° C. for 2 hours(step S112).

Then, onto the thermoplastic liquid crystal polymer solution-coateddried copper foil passed through the coating section, a thermoplasticliquid crystal polymer film having a thickness of, for example, 25 μm, athermal deformation temperature of, for example, 260° C., and a meltingpoint of, for example, 283° C., fed from the thermoplastic liquidcrystal polymer film feed roll, is thermally pressed by the heatingrolls at a temperature of 270° C., a speed of 1 m/minute, and a pressureof 3 MPa, thus making a copper clad laminate having a uniform thicknessof, for example, 45 μm (steps S114 and S116).

The peel strength of the copper clad laminate manufactured using theabove-described embodiment of the present invention was measuredaccording to IPC-TM-650 2.4.8, and the result is shown in Table 1 below.In Table 1, comparative example 1 is a measurement result according toIPC-TM-650 2.4.8 for the peel strength of a copper clad laminatemanufactured by thermally pressing a thermoplastic liquid crystalpolymer film (melting point: 309° C.) onto a 12-μm-thick copper foilhaving rough (Rz: 2 μm) surface. Comparative example 2 is a measurementresult according to IPC-TM-650 2.4.8 for the peel strength of a copperclad laminate manufactured by thermally pressing a thermoplastic liquidcrystal polymer film (thermal deformation temperature: 275° C., andmelting point: 295° C.) onto a 18-m-thick copper foil having a rough(Rz: 2 μm) surface. TABLE 1 Comparative Comparative Invention example 1example 2 Peel strength (kN/m) 0.8 0.33 0.3 Measurement method IPC 2.4.8IPC 2.4.8 IPC 2.4.8

As can be seen in Table 1, the measured peel strengths were 0.8 kN/m forthe inventive embodiment, 0.33 kN/m for comparative example 1, and 0.3kN/m for comparative example 2, indicating that the inventive embodimentshowed a great improvement in peel strength.

As described above, according to the present invention, the copper foilhaving a rough surface and the thermoplastic liquid crystal polymersolution are used to solve the problem of low peel strength in the priorcopper clad laminate manufactured by the thermal pressing between athermoplastic liquid crystal polymer and a copper foil. Also, thelamination of the thermoplastic liquid crystal polymer film by thermalpressing with the heating rolls is carried out to solve the problems ofnon-uniform thickness and the occurrence of curling which can occur uponcoating. Accordingly, the present invention allows the manufacturing ofa copper clad laminate having high peel strength, a flat surface, anduniform thickness, and at the same time, no curling problem.

Also in view of improved peel strength, the inventive copper cladlaminate can be applicable to flexible and rigid-flexible printedcircuit boards, and the rough copper foil surface, in the manufacturingof multilayer PCBs, will make a lamination process easy.

Although an embodiment of the present invention has been described forillustrative purposes, those skilled in the art will appreciate thatvarious modifications, additions and substitutions are possible, withoutdeparting from the scope and spirit of the invention as disclosed in theaccompanying claims.

1. An apparatus for manufacturing a copper clad laminate, comprising: acoating device for thinly coating a surface of a copper foil with athermoplastic liquid crystal polymer solution; a solvent removal devicefor drying the coated liquid crystal polymer solution to remove thesolvent of the coated polymer solution; and a thermal pressing devicefor laminating and thermally pressing a thermoplastic liquid crystalpolymer film onto the copper foil.
 2. The apparatus of claim 1, whereinthe coating device comprises: a coating section coating thethermoplastic liquid crystal polymer solution onto the copper foilhaving a roughness formed thereon to coat the copper foil; and copperfoil transfer rolls transferring a copper foil fed from a copper feedroll to the coating section.
 3. The apparatus of claim 1, wherein thesolvent removal device comprises a heating section removing the solventby pre-drying at a first temperature for a first predetermined time, andcompletely drying at a second temperature for a second predeterminedtime.
 4. The apparatus of claim 3, wherein the first temperature is50-1,000° C., the first predetermined time is 30 minutes to 2 hours, thesecond temperature is 250-300° C., and the second predetermined time is1-4 hours.
 5. The apparatus of claim 1, wherein the thermal pressingdevice comprises heating rolls to make the copper clad laminate bythermal pressing at a temperature higher than the thermal deformationtemperature of the polymer film, a speed of 1-5 m/minute, and a pressureof 1-10 MPa.
 6. The apparatus of claim 1, wherein the thermoplasticliquid crystal polymer solution includes a filler for reducing thecoefficient of thermal expansion.
 7. A method for manufacturing a copperclad laminate, comprising the steps of: thinly coating a surface of acopper foil having a roughness formed thereon with a thermoplasticliquid crystal polymer solution; drying the coated liquid crystalpolymer solution to remove the solvent of the thermoplastic liquidcrystal polymer solution; and laminating and thermally pressing athermoplastic liquid crystal polymer film onto the copper foil byheating rolls.
 8. The method of claim 7, wherein the thinly coating stepcomprises the steps of: transferring the copper foil fed from a copperfoil feed roll to a coating section; and coating the thermoplasticliquid crystal polymer solution onto the copper foil having theroughness formed thereon to coat the copper foil.
 9. The method of claim7, wherein the drying step comprises the steps of: pre-drying thepolymer solution coated on the copper foil at a first temperature for afirst predetermined time using a solvent removal device; and completelydrying the polymer solution coated on the copper foil at a secondtemperature for a second predetermined time to remove the solvent of thepolymer solution.
 10. The method of claim 7, wherein the thermalpressing in the laminating and thermally pressing step is carried out ata temperature higher than the thermal deformation temperature of thepolymer film, a speed of 1-5 m/minute, and a pressure of 1-10 MPa. 11.The method of claim 7, wherein the thermoplastic liquid crystal polymersolution includes a filler for reducing the coefficient of thermalexpansion.